Pulse source arrangement



Feb. 15, 1966 J. G. BAUWENS PULSE SOURCE ARRANGEMENT Filed NOV. 22, 1961Inventor I BA U WENS United States Patent 3,235,841 PULSE SOURCEARRANGEMENT Jan G. Bauwens, Antwerp, Belgium, assignor to InternationalStandard Electric Corporation, New York, N.Y., a corporation of DelawareFiled Nov. 22, 1961, Ser. No. 154,298 Claims priority, applicationNetherlands, Dec. 1, 1969, 258,569 7 Claims. (Cl. 340-166) Thisinvention relates to a pulse source arrangement and more particularly toa transistorized pulse source comprising electromagnetic devices.

Such pulse sources are already known. For example, it is well known toprovide pulse sources comprising a charging resistor, self inductioncoil, and switching means such as a transistor switch, all connected inseries between a potential source and ground. The self induction coil iscoupled to a load impedance. These known sources further include meansfor periodically switching the transistor between a conducting and anon-conducting state.

Difliculties have been encountered in the use of these prior art pulsesources; among other things, the load current is dependent on the loadand accordingly current flowing in the load exponentially decreases orincreases as a function of the load variations. Also, the prior artarrangements further have the disadvantage that the load current may notbe made much larger than the charging current.

It is therefore an object of the present invention to provide a pulsesource arrangement which is able to supply to a load a current whichalways decreases independent of the load.

It is another object of the present invention to provide a currentsource arrangement which is able to supply to a load a constant currentindependent of the load.

It is still another object of the present invention to pro vide a pulsesource arrangement which enables current pulses having a higheramplitude than the output current to be fed to a load.

The pulse source arrangement according to the invention is characterizedby the fact, that said self-induction coil constitutes the primarywinding of a transformer, the secondary Winding of which is coupled to aload via a unidirectional device. The primary winding is seriesconnected between a charging resistor and a switching device. The seriescombination is, in turn, connected between a first and a second DC.potential. When the said switching means is periodically operated andreleased, the induction coil is charged and discharged respectively.Thus, magnetic energy is periodically stored in said primary Winding andperiodically transferred to said secondary winding to produce outputpulses therein that are independent of the load.

The above mentioned and other objects and features of the invention willbecome more apparent and the invention itself will be best understood byreferring to the following description of embodiments taken inconjunction with the accompanying drawings wherein:

FIG. 1 represents a pulse source arrangement according to the invention;

FIG. 2 shows a two-coordinate selection matrix Wherein the pulse sourcearrangement according to the invention is used.

Principally referring to FIG. 1, a charging resistor R, the primarywinding L, of a transformer T and a transistor switch T are connected inseries between the terminals of a DC. voltage source E the positiveterminal of which is grounded. The emitter and the collector of thetransistor T are respectively connected to the above ground and to thelower end of the above primary winding L whereas the base of transistorT is controlled by a control device indicated by the positive inputpulse 10. The secondary winding L of the above transformer T isconnected to a load impedance Z via a unidirectional transistor switch Tthe base electrode of which is also controlled by the above controldevice as indicated by negative pulse 11, which alternately andperiodically renders conductive and blocks the transistors T and Trespectively during a charging interval T These conductive and blockedconditions are reversed during a so called pulse interval T The ratio ofthe number of turns of the primary winding to the number of turns of thesecondary winding is indicated by the reference letter m.

During the charging interval T magnetic energy is stored in the primarywinding L of the transformers T, and the charging current i in thisprimary winding exponentially varies towards the final value At the endof the charging interval T and hence at the start of a pulse interval Tthe charging current i, has reached the value I so that the magneticenergy stored in the core 'of the transformer T is equal to LIIIOZ 2This energy will induce a voltage across the windings of the transformerin order to force a transient current to flow of such an amplitude thatthere is no instantaneous change of the ampere turns applied to thecore. When the transistor T is conductive an induced voltage will beapplied to the load so as to cause a current to flow therein and a backvoltage will appear at the primary side of the transformer. This backvoltage swings the collector of the transistor T down to a voltage whichis larger than E with a maximum of E This voltage E must fall within thevoltage rating of the transistor T The induced current i flowing in thesecondary winding of the transformer T is a transient current whichcannot maintain indefinitely. Indeed, it is equal to current t I E I nta-ah wherein t, is the time constant of the charging circuit.

Hence one may write for the above value Where v is the voltage across Lduring the pulse interval T As stated above, the above output current ivaries from I to I during this pulse interval T so that one may writewherein L is the constant inductance of the secondary winding of thetransformer T and of the load. .Hence Tp J2 vdt L2: I1 I2 In order tohave a current source, I that is independent of the load, the secondterm must be negligible with regard to the first, i.e.

in other words, the relative current drop in the secondary winding mustbe much smaller than Since the latter term can never be negative it isclear that the end-value 1 of the output circuitwill always be smallerthan its initial value I Such a current source is especially desirablein the case of magnetic core switching since quasi-rectangular pulsesare then needed.

If the load is however, formed by a transistor which must be renderedconductive at the start of an impulse T it is not necessary that thedriving pulses are rectangular since only the initial current should besuflicient to force this transistor quickly in the conducting state.

In this case it is also not necessary to provide a unidirectional devicesuch as the transistor T in FIGURE 1, as

the load transistor itself constitutes the unidirectional device.

From the above Formula 3 it'follows that in order to realize a linearcurrent drop in the load transistor it is sufficient that the chargingtime interval T, be much smaller than the time constant t of thecharging circuit.

With regard to a load transistor it should be remarked that thistransistor can be cut-off very quickly at the end of the pulse T by theaddition of a capacitor across the charging resistor R. Indeed, as thiscapacity is discharged through the resistance R during the pulse T theresistance R does not play a role at the first moment the transistor Tis again rendered conductive. Due to 4 this a reverse voltage isdeveloped in the secondary wind ing which reaches the valueinstantaneously, so that the load transistor is cut-off very quickly.

Principally referring to FIG. 2, the above described pulse source isused for controlling the speech gates in an electronic telephoneexchange. Each of these speech gates is constituted by a PNP transistorT and all these transistors are arranged in two-coordinate matriceshaving each e.g. a capacity of 10x10 for a group of subscribers.

Each transistor T is connected to one end of the secondary winding L ofthe associated transformer T which may be called a cross-pointtransformer and the other end of this secondary winding is connected tothe positive terminal of a DC. potential source E the negative terminalof which is grounded.

The different primary windings L of all the crosspoint transformers T ofa column are connected in series with the charging resistor R and thecolumn transistor switch formed by PNP transistor T (first switchingmeans), between ground and the negative terminal of the DC. source EEach cross-point transformer further includes a tertiary winding L andall the tertiary windings of a row are connected, via an individualdiode rectifier d, to the collector of a common row PNP transistorswitch T (second switching means) the emitter of which is grounded. Theother ends of the different tertiary windings are also grounded.

The driving of this matrix is asfollows. Suppose that the loadtransistor T on the cross-point of the first column and the first rowmust be rendered conductive.

Normally the column and row transistors T and T are conductive, so thatmagnetic energy is stored in all the primary windings of all thetransformers belonging to the first column, whereas the tertiarywindings of all the transformers included in the first row are short--circuited.

At the moment the transistor T must be rendered con ductive, both firstand second switching means transistors T and T are blocked during a timeinterval T thus liberating the magnetic energy stored in the primarywindings of the column considered.

The transfer of energy from these primary windings towards theassociated secondary windings will however only be possible for thecross-point transformer T since all the other tertiary windings of thecross-point transformers of the column considered are short-circuited.

The high back current needed to switch oif the transistor T quickly isnow delivered mainly by the rowtransistor T short-circuiting again thetertiary winding of the transformer T at the end of the time interval TIndeed, at that moment the base of the transistor T sees a very lowimpedance and is practically shortcircuited to the positive bias E Fromthe above itfollows that the described pulse source arrangement isparticularly adapted for the control of electronic gates and especiallyfor the control of the speech gates in a full electronic telephoneexchange. Indeed during the above pulse intervals T current is deliveredto the base of the transistors, constituting said speech gates, from ahigh impedance source whereas the impedance in the base circuit of thesetransistors is very low during the charging intervals due to the abovetertiary windings being short-circuited.

In order to prevent a high reverse voltage to appear at the secondarywinding of the transformer at the end of the pulse interval T thissecondary winding may be shunted by a diode in series With a resistance.This diode should be arranged in such a manner that it becomesconductive at theend of the above interval T While the principles of theinvention have been described above in connection with specificapparatus, it is to be clearly understood that this description is madeonly by way of example and not as a limitation on the scope of theinvention.

I claim:

1. A pulse source circuit comprising a DC. battery potential source andground, transformer means; a series circuit comprising resistor means, afirst winding of said transformer means and normally conductingswitching means, connected between said battery and ground; loadimpedance coupled to a secondary winding of said transformer,unidirectional means in series between said secondary winding and saidload impedance means, means for periodically operating said switchingmeans, whereby said switching means is periodically blocked toperiodically transfer magnetic energy stored in said first winding tosaid secondary winding for producing output pulses across saidsecondarywinding, and means for operating said unidirectional means toconduct said output pulses through said unidirectional means to saidload impedance.

2. The pulse source circuit of claim 1 wherein said unidirectionaldevice is a transistor gate.

3. The pulse source circuit of claim 2 wherein said operating meansprovide a pulse having a length much smaller than the time constant ofthe series circuit.

4. The pulse source circuit of claim 2 wherein the said first winding isalso coupled to a tertiary winding and said tertiary winding is branchedin a closed circuit with a second switching means and is connected inseries with a second unidirectional device.

5. The pulse source circuit of claim 1 having said secondary windingshunted by another series circuit comprising a third unidirectionaldevice and a second resistor, said third unidirectional device beingpoled to be conductive at the end of said operating pulse.

6. The pulse source circuit of claim 1 wherein the relative current dropin said secondary winding during said transfer period is much smallerthan the ratio of operating pulse length over the quantity 2 raised tothe power of the time constant of said series circuit minus one, wherebythe current supplied by said pulse source circuit is independent of saidload and said output pulses are substantially rectangular.

7. A plurality of pulse source circuits as claimed in claim 6 forselectively producing pulses across loads, characterized in this, thatsaid circuits include a number of three-winding crosspoint transformerswhich are arranged in a two-coordinate matrix comprising rows andcolumns, means for arranging the primary windings of the transformers inthe same column of said matrix connected in series and associated to oneof said pulse sources through said switching means, means for arrangingeach of the tertiary windings of the transformers are arranged in a samerow of said matrix coupled to said second switching means, means forconnecting the tertiary winding of said transformers in series with saidloads, one of said second switching means being provided in common forthe transformers of each of said rows, via another individualunidirectional device, and means for selectively simultaneously blockingthe said first and second switching means associated with a desired oneof said loads.

References Cited by the Examiner UNITED STATES PATENTS 2,902,677 9/ 1959Counihan 340166 2,917,727 12/ 1959 Reach 34O166 2,947,977 8/ 1960 Bloch340-166 2,968,029 1/1961 Grosser 340-466 3,015,808 1/1962 De Troye340-166 NEIL C. READ, Primary Examiner.

IRVING L. SRAGOW, Examiner.

1. A PULSE SOURCE CIRCUIT COMPRISING A D.C. BATTERY POTENTIAL SOURCE ANDGROUND, TRANSFORMER MEANS; A SERIES CIRCUIT COMPRISING RESISTOR MEANS, AFIRST WINDING OF SAID TRANSFORMER MEANS AND NORMALLY CONDUCTINGSWITCHING MEANS, CONNECTED BETWEEN SAID BATTERY AND GROUND; LOADIMPEDANCE COUPLED TO A SECONDARY WINDING OF SAID TRANSFORMER,UNIDIRECTIONAL MEANS IN SERIES BETWEEN SAID SECONDARY WINDING AND SAIDLOAD IMPEDANCE MEANS, MEANS FOR PERIODICALLY OPERATING SAID SWITCHINGMEANS, WHEREBY SAID SWITCHING MEANS IS PERIODICALLY BLOCKED TOPERIODICALLY TRANSFER MAGNETIC ENERGY STORED IN SAID FIRST WINDING TOSAID SECONDARY WINDING FOR PRODUCING OUTPUT PULSES ACROSS SAID SECONDARYWINDING, MEANS FOR OPERATING SAID UNIDIRECTIONAL MEANS TO CONDUCT SAIDOUTPUT PULSES THROUGH SAID UNIDIRECTIONAL MEANS TO SAID LOAD IMPEDANCE.6. THE PULSE SOURCE CIRCUIT OF CLAIM 1 WHEREIN THE RELATIVE CURRENT DROPIN SAID SECONDARY WINDING DURING SAID TRANSFER PERIOD IS MUCH SMALLERTHAN THE RATIO OF OPERATING PULSE LENGTH OVER THE QUANTITY E RAISED TOTHE POWER OF THE TIME CONSTANT OF SAID SERIES CIRCUIT MINUS ONE, WHEREBYTHE CURRENT SUPPLIED BY SAID PULSE SOURCE CIRCUIT IS INDEPENDENT OF SAIDLOAD AND SAID OUTPUT PULSES ARE SUBSTANTIALLY RECTANGULAR.
 7. APLURALITY OF PULSE SOURCE CIRCUITS AS CLAIMED IN CLAIM 6 FOR SELECTIVELYPRODUCING PULSES ACROSS LOADS, CHARACTERIZED IN THIS, THAT SAID CIRCUITSINCLUDE A NUMBER OF THREE-WINDING CROSSPOINT TRANSFORMER WHICH AREARRANGED IN A TWO-COORDINATE MATRIX COMPRISING ROWS AND COLUMNS, MEANSFOR ARRANGING THE PRIMARY WINDINGS OF THE TRANSFORMER IN THE SAME COLUMNOF SAID MATRIX CONNECTED IN SERIES AND ASSOCIATED TO ONE OF SAID PULSESOURCES THROUGH SAID SWITCHING MEANS, MEANS FOR ARRANGING EACH OF THETERTIARY WINDINGS OF THE TRANSFORMERS ARE ARRANGED IN A SAME ROW OF SAIDMATRIX COUPLED TO SAID SECOND SWITCHING MEANS, MEANS FOR CONNECTING THETERTIARY WINDING OF SAID TRANSFORMERS IN SERIES WITH SAID LOADS, ONE OFSAID SECOND SWITCHING MEANS BEING PROVIDED IN COMMON FOR THETRANSFORMERS OF EACH OF SAID ROWS, VIA ANOTHER INDIVIDUAL UNIDIRECTIONALDEVICE, AND MEANS FOR SELECTIVELY SIMULTANEOUSLY BLOCKING THE SAID FIRSTAND SECOND SWITCHING MEANS ASSOCIATED WITH A DESIRED ONE OF SAID LOADS.